FINITE DEFORMATION AND DISPLACEMENT-FIELDS ON THE SOUTHERN YEMEN MARGIN USING SATELLITE IMAGES, TOPOGRAPHIC DATA AND A RESTORATION METHOD

Geological interpretations of processed satellite images and structura l field measurements were used to calculate the amount of extension an d the finite displacement field of two stretched areas located on the northern margin of the Gulf of Aden, in Yemen. This calculation was do ne by a comparison between the deformed and the undeformed states of e ach studied area. The structural setting established from satellite-im age interpretations and fieldwork yields a detailed geometry of the de formed state. The undeformed state was reconstructed from reference la yers chosen on satellite images from folded and faulted geological mar kers. The strike and dip of those layers were computed directly from d ip indicator measurements, identified on three-dimensional (3D) realis tic views of the sites (derived from SPOT stereoscopic views and topog raphic data) and controlled by field measurements. From the previous s tructural data, a numerical model of the deformed state was prepared w ith respect to the structural setting. The two stretched areas were th en restored to their undeformed state successively by (1) an unfolding method (use of the UNFOLD program on each folded piece bounded by fau lts), and (2) a best-fit method (fitting along the boundary of the unf olded pieces). The comparison between the deformed and undeformed stat es leads to quantifying the amount of strain and to establishing the t otal finite displacement field. The results point to differences in th e amount of extension and in the finite displacement field between the two areas studied. Within the regional context of the Afar triple jun ction kinematics, this leads to the conclusion that there was an early extensional tectonic phase recorded on the southern Yemen margin, pro bably linked to the earlier opening of the Gulf of Aden.